This study is to describe the exact location of NOAF-maintaining foci and rotors after cardiac surgery identified by mapping using the non-invasive phase mapping with CardioInsightTM - 3D Mapping technology (CardioInsightTM, Medtronic Switzerland, Tolochenaz, Switzerland) and a low-dose computed tomography scan of the chest.

Atrial fibrillation (AF) is the most commonly oberserved postoperative complication after cardiac surgery. New-onset atrial fibrillation (NOAF) leads to prolonged intensive care unit (ICU) and hospital length of stay, increased early mortality and stroke along with higher treatment costs.

The exact location of structures triggering or maintaining NOAF is unknown. Identifying the exact location of NOAF- maintaining foci and rotors could allow development of preventive treatment strategies like preoperative ablation or perioperative ablation of high-risk foci. Non-invasive phase mapping with CardioInsightTM (CIT) - 3D Mapping technology (CardioInsightTM, Medtronic Switzerland, Tolochenaz, Switzerland) allows non-invasive description of AF foci and rotors with a 252-electrode vest applied to the patient's torso due to detailed mapping of NOAF-maintaining structures without invasive electrophysiological examination.

This study is to describe the exact location of NOAF-maintaining foci and rotors after cardiac surgery identified by mapping using the non-invasive phase mapping with CardioInsightTM - 3D Mapping technology (CardioInsightTM, Medtronic Switzerland, Tolochenaz, Switzerland) and a low-dose computed tomography scan of the chest.

Inclusion Criteria:

• Cardiac surgery
• Signed informed consent by patient or next of kin

Mapping inclusion criteria

• NOAF within the first seven postoperative days (168 hours) after cardiac surgery developing on the cardiac surgery ward, intermediate care unit or the intensive care unit of the University Hospital Basel. ICU admission will be set as starting point for observation time.

General Exclusion Criteria:

Preoperative conditions:

• History of previous left atrial ablation
• History of cardioembolic stroke
• History of amiodarone treatment within three months
• Any documented history of atrial fibrillation/atrial flutter before surgery
• Left ventricular ejection fraction <40%
• Patient included into other study with radiation exposure

Perioperative conditions

• Perioperative mechanical circulatory support (e.g., intraaortic balloon pump; extracorporeal membrane oxygenation; left ventricular assist device (e.g. Impella, Abiomed Inc., Aachen, Germany)

Mapping exclusion criteria

• Heart rate ≥ 50 bpm AND contraindication to adenosine.

Contraindications to adenosine:

• Allergy/intolerance to adenosine
• History of chronic obstructive pulmonary disease (COPD Gold IV)(28)
• History of asthma
• History of Long-QT syndrome
• Hemodynamically unstable patients (margin of discretion of the attending physician)

Ongoing recruitment of elective and emergent patients through the study team will be performed during daily practice. All patients referred to the Department of Cardiac Surgery, University Hospital Basel, are routinely informed about the potential complication of NOAF. Besides, patients are informed about the BigMap study, mapping with CIT, its indications and contraindications. All patients who have given informed consent before surgery and present with NOAF are monitored and the mapping procedure is performed.